System and method for delivering modulated sub-threshold therapy to a patient

ABSTRACT

A neuromodulation system configured for providing sub-threshold neuromodulation therapy to a patient. The neuromodulation system comprises a neuromodulation lead having at least one electrode configured for being implanted along a spinal cord of a patient, a plurality of electrical terminals configured for being respectively coupled to the at least one electrode, modulation output circuitry configured for delivering sub-threshold modulation energy to active ones of the at least one electrode, and control/processing circuitry configured for selecting a percentage from a plurality of percentages based on a known longitudinal location of the neuromodulation lead relative to the spinal cord, computing an amplitude value as a function of the selected percentage, and controlling the modulation output circuitry to deliver sub-threshold modulation energy to the patient at the computed amplitude value.

CLAIM OF PRIORITY

This application is a continuation of U.S. application Ser. No.15/199,080, filed Jun. 30, 2016, now issued as U.S. Pat. No. 9,844,674,which is a continuation of U.S. application Ser. No. 14/601,686, filedJan. 21, 2015, now issued as U.S. Pat. No. 9,381,359, which claims thebenefit of priority under 35 U.S.C. § 119(e) of U.S. Provisional PatentApplication Ser. No. 61/936,273, filed on Feb. 5, 2014, each of which isherein incorporated by reference in its entirety.

FIELD OF THE INVENTION

The present inventions relate to tissue modulation systems, and moreparticularly, to programmable neuromodulation systems.

BACKGROUND OF THE INVENTION

Implantable neuromodulation systems have proven therapeutic in a widevariety of diseases and disorders. Pacemakers and Implantable CardiacDefibrillators (ICDs) have proven highly effective in the treatment of anumber of cardiac conditions (e.g., arrhythmias). Spinal CordStimulation (SCS) systems have long been accepted as a therapeuticmodality for the treatment of chronic pain syndromes, and theapplication of tissue stimulation has begun to expand to additionalapplications such as angina pectoralis and incontinence. Deep BrainStimulation (DBS) has also been applied therapeutically for well over adecade for the treatment of refractory chronic pain syndromes, and DBShas also recently been applied in additional areas such as movementdisorders and epilepsy. Further, in recent investigations, PeripheralNerve Stimulation (PNS) systems have demonstrated efficacy in thetreatment of chronic pain syndromes and incontinence, and a number ofadditional applications are currently under investigation. Furthermore,Functional Electrical Stimulation (FES) systems, such as the Freehandsystem by NeuroControl (Cleveland, Ohio), have been applied to restoresome functionality to paralyzed extremities in spinal cord injurypatients.

These implantable neuromodulation systems typically include one or moreelectrode carrying stimulation leads, which are implanted at the desiredstimulation site, and an implantable neuromodulation device (e.g., animplantable pulse generator (IPG)) implanted remotely from thestimulation site, but coupled either directly to the neuromodulationlead(s) or indirectly to the neuromodulation lead(s) via a leadextension. The neuromodulation system may further comprise a handheldexternal control device (e.g., a remote control (RC)) to remotelyinstruct the neuromodulator to generate electrical stimulation pulses inaccordance with selected stimulation parameters.

Electrical modulation energy may be delivered from the neuromodulationdevice to the electrodes in the form of an electrical pulsed waveform.Thus, electrical energy may be controllably delivered to the electrodesto therapeutically modulate neural tissue. The configuration ofelectrodes used to deliver electrical pulses to the targeted tissueconstitutes an electrode configuration, with the electrodes capable ofbeing selectively programmed to act as anodes (positive), cathodes(negative), or left off (zero). In other words, an electrodeconfiguration represents the polarity being positive, negative, or zero.Other parameters that may be controlled or varied include the amplitude,width, and rate of the electrical pulses (which may be consideredelectrical pulse parameters) provided through the electrode array. Eachelectrode configuration, along with the electrical pulse parameters, canbe referred to as a “modulation parameter set.”

With some neuromodulation systems, and in particular, those withindependently controlled current or voltage sources, the distribution ofthe current to the electrodes (including the case of the neuromodulationdevice, which may act as an electrode) may be varied such that thecurrent is supplied via numerous different electrode configurations. Indifferent configurations, the electrodes may provide current or voltagein different relative percentages of positive and negative current orvoltage to create different electrical current distributions (i.e.,fractionalized electrode configurations).

As briefly discussed above, an external control device can be used toinstruct the neuromodulation device to generate electrical pulses inaccordance with the selected modulation parameters. Typically, themodulation parameters programmed into the neuromodulation device can beadjusted by manipulating controls on the handheld external controldevice to modify the electrical modulation energy provided by theneuromodulation device system to the patient. Thus, in accordance withthe modulation parameters programmed by the external control device,electrical pulses can be delivered from the neuromodulation device tothe electrode(s) to modulate a volume of tissue in accordance with a setof modulation parameters and provide the desired efficacious therapy tothe patient. The best modulation set will typically be one that deliversmodulation energy to the volume of tissue that must be modulated inorder to provide the therapeutic benefit (e.g., treatment of pain),while minimizing the volume of non-target tissue that is modulated.

However, the number of electrodes available combined with the ability togenerate a variety of complex electrical pulses, presents a hugeselection of modulation parameter sets to the clinician or patient. Forexample, if the neuromodulation system to be programmed has an array ofsixteen electrodes, millions of modulation parameter sets may beavailable for programming into the neuromodulation system. Today,neuromodulation systems may have up to thirty-two electrodes, therebyexponentially increasing the number of modulation parameters setsavailable for programming.

To facilitate such selection, the clinician generally programs theneuromodulation device through a computerized programming system. Thisprogramming system can be a self-contained hardware/software system, orcan be defined predominantly by software running on a standard personalcomputer (PC). The PC or custom hardware may actively control thecharacteristics of the electrical stimulation generated by theneuromodulation device to allow the optimum stimulation parameters to bedetermined based on patient feedback or other means and to subsequentlyprogram the neuromodulation device with the optimum modulation parametersets.

For example, in order to achieve an effective result from conventionalSCS, the lead or leads must be placed in a location, such that theelectrical modulation energy (in this case, electrical stimulationenergy) creates a sensation known as paresthesia, which can becharacterized as an alternative sensation that replaces the pain signalssensed by the patient. The paresthesia induced by the stimulation andperceived by the patient should be located in approximately the sameplace in the patient's body as the pain that is the target of treatment.If a lead is not correctly positioned, it is possible that the patientwill receive little or no benefit from an implanted SCS system. Thus,correct lead placement can mean the difference between effective andineffective pain therapy. When electrical leads are implanted within thepatient, the computerized programming system, in the context of anoperating room (OR) mapping procedure, may be used to instruct theneuromodulation device to apply electrical stimulation to test placementof the leads and/or electrodes, thereby assuring that the leads and/orelectrodes are implanted in effective locations within the patient.

Once the leads are correctly positioned, a fitting procedure, which maybe referred to as a navigation session, may be performed using thecomputerized programming system to program the external control device,and if applicable the neuromodulation device, with a set of modulationparameters that best addresses the painful site. Thus, the navigationsession may be used to pinpoint volume of activation (VOA) or areascorrelating to the pain. Such programming ability is particularlyadvantageous for targeting the tissue during implantation, or afterimplantation should the leads gradually or unexpectedly move that wouldotherwise relocate the stimulation energy away from the target site. Byreprogramming the neuromodulation device (typically by independentlyvarying the stimulation energy on the electrodes), the volume ofactivation (VOA) can often be moved back to the effective pain sitewithout having to re-operate on the patient in order to reposition thelead and its electrode array. When adjusting the volume of activation(VOA) relative to the tissue, it is desirable to make small changes inthe proportions of current, so that changes in the spatial recruitmentof nerve fibers will be perceived by the patient as being smooth andcontinuous and to have incremental targeting capability.

Although alternative or artifactual sensations are usually toleratedrelative to the sensation of pain, patients sometimes report thesesensations to be uncomfortable, and therefore, they can be considered anadverse side-effect to neuromodulation therapy in some cases. Becausethe perception of paresthesia has been used as an indicator that theapplied electrical energy is, in fact, alleviating the pain experiencedby the patient, the amplitude of the applied electrical energy isgenerally adjusted to a level that causes the perception of paresthesia.It has been shown, however, that the delivery of sub-thresholdelectrical energy (e.g., high frequency pulsed electrical energy and/orlow pulse width electrical energy) can be effective in providingneuromodulation therapy for chronic pain without causing paresthesia.

Although sub-threshold modulation therapies have shown good efficacy inearly studies, because there is a lack of paresthesia that may otherwiseindicate that the delivered sub-threshold electrical energy isoptimized, or at least efficacious, it is difficult to immediatelydetermine if the delivered sub-threshold therapy is optimized in termsof providing efficacious therapy. Given that the user cannot rely on thepatient's perception of paresthesia, it is often difficult to find thepulse amplitude for the patient that neither under-stimulates thetargeted tissue nor accidentally causes the sensation of paresthesia.Thus, finding the optimal set of modulation parameters, especially pulseamplitude, for sub-threshold modulation therapy is often time-consumingand tedious.

There, thus, remains a need to provide a more efficient means todetermine the appropriate pulse amplitude for sub-threshold modulationtherapy.

SUMMARY OF THE INVENTION

In accordance with a first aspect of the present inventions, atherapeutic neuromodulation system is provided. The neuromodulationsystem comprises a neuromodulation lead having at least one electrodeconfigured for being implanted along a spinal cord of a patient, aplurality of electrical terminals configured for being respectivelycoupled to at least one electrode, modulation output circuitryconfigured for delivered sub-threshold modulation energy (e.g., pulsewidth less than 100 μs, pulse rate greater than 1500 Hz, etc.) to activeones of the at least one electrode, and control/processing circuitryconfigured for selecting a percentage from a plurality of percentagesbased on a known longitudinal location of the neuromodulation leadrelative to the spinal cord, computing an amplitude value as a functionof the selection percentage, and controlling the modulation outputcircuitry to deliver sub-threshold modulation energy to the patient atthe computed amplitude value.

The selected percentage is a first percentage if the longitudinallocation is in a first region of the spinal cord, and the selectedpercentage is a second percentage if the longitudinal location is in asecond region of the spinal cord, wherein the second percentage ishigher than the first percentage, and the second region of the spinalcord is caudal to the first region of the spinal cord.

The selected percentage may be a first percentage (20%-60%) if thelongitudinal location is in a cervical region of the spinal cord, asecond percentage (30%-70%) if the longitudinal location is in athoracic region of the spinal cord, a third percentage (40%-80%) if thelongitudinal location is in a lumbar region of the spinal cord, and afourth percentage (50%-90%) if the longitudinal location is in a sacralregion of the spinal cord. The second percentage is greater than thefirst percentage, the third percentage is greater than the secondpercentage, and the fourth percentage is greater than the thirdpercentage.

The control/processing circuitry is configured for computing theamplitude value as a function of the selected percentage and aperception threshold of the patient.

The neuromodulation system further comprises memory configured forstoring a look-up table containing a plurality of different percentagesand associated neuromodulation lead locations. The percentage isselected by matching the known longitudinal location of theneuromodulation lead relative to the spinal cord with one of theneuromodulation lead locations stored in the look-up table.

The control/processing circuitry may be configured for determining theknown longitudinal location of the implanted neuromodulation leadrelative to the spinal cord. In an alternate embodiment, theneuromodulation system further comprises a user interface configured forreceiving user input defining the known longitudinal location of theimplanted neuromodulation lead relative to the spinal cord.

In accordance with a second aspect of the present inventions, anexternal controller for user with a neuromodulation device coupled to atleast one electrode comprising a user interface configured for receivinguser input, control/processing circuitry configured for selecting apercentage from a plurality of percentages based on a known longitudinallocation of the neuromodulation lead relative to the spinal cord,computing an amplitude value as a function of the selected percentageand output circuitry configured for transmitting the amplitude value tothe neuromodulation device.

The amplitude value is computed in the same manner described above. Thepercentages are selected in the same manner described above. Thelongitudinal location of the neuromodulation lead is determined in thesame manner described above.

In accordance to a third aspect of the present inventions, a method ofproviding sub-threshold modulation therapy to a patient comprisesselecting a percentage from a plurality of percentages based on a knownlongitudinal location of the neuromodulation lead relative to the spinalcord, computing an amplitude value as a function of the selectedpercentage, and delivering sub-threshold modulation energy to thepatient at the computed amplitude value.

The method of computing the amplitude value is computed is the same asdescribed above. The method of selecting percentages based on thelongitudinal location is the same as described above. The longitudinallocation of the neuromodulation lead is determined in the same mannerdescribed above.

Other and further aspects and features of the invention will be evidentfrom reading the following detailed description of the preferredembodiments, which are intended to illustrate, not limit, the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate the design and utility of preferred embodimentsof the present invention, in which similar elements are referred to bycommon reference numerals. In order to better appreciate how theabove-recited and other advantages and objects of the present inventionsare obtained, a more particular description of the present inventionsbriefly described above will be rendered by reference to specificembodiments thereof, which are illustrated in the accompanying drawings.Understanding that these drawings depict only typical embodiments of theinvention and are not therefore to be considered limiting of its scope,the invention will be described and explained with additionalspecificity and detail through the use of the accompanying drawings inwhich:

FIG. 1 is a plan view of a Spinal Cord Modulation (SCM) systemconstructed in accordance with one embodiment of the present inventions;

FIG. 2 is a plan view of the SCM system of FIG. 1 in use with a patient;

FIG. 3 is a profile view of an implantable pulse generator (IPG) andpercutaneous leads used in the SCM system of FIG. 1;

FIG. 4 is a plot of monophasic cathodic electrical modulation energy;

FIG. 5a is a plot of biphasic electrical modulation energy having acathodic modulation pulse and an active charge recovery pulse;

FIG. 5b is a plot of biphasic electrical modulation energy having acathodic modulation pulse and a passive charge recovery pulse;

FIG. 6 is a block diagram of a clinician's programmer (CP) used in theSCM system of FIG. 1;

FIG. 7 is a plan view of a user interface of the CP of FIG. 6 forprogramming the IPG of FIG. 3 in a manual programming mode;

FIG. 8 is a plan view of a user interface of the CP of FIG. 6illustrating a perception threshold program screen for determining aperception threshold;

FIG. 9 is a table illustrating a plurality of percentages of theperception threshold based on a longitudinal location of the implantedneuromodulation lead of FIG. 3 with respect to the spinal cord; and

FIG. 10 is the plan view of the manual programming mode of FIG. 7illustrating the automatically selected sub-threshold amplitude based onthe table of FIG. 9.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The description that follows relates to a spinal cord modulation (SCM)system. However, it is to be understood that the while the inventionlends itself well to applications in SCM, the invention, in its broadestaspects, may not be so limited. Rather, the invention may be used withany type of implantable electrical circuitry used to stimulate tissue.For example, the present invention may be used as part of a pacemaker, adefibrillator, a cochlear stimulator, a retinal stimulator, a stimulatorconfigured to produce coordinated limb movement, a cortical stimulator,a deep brain stimulator, peripheral nerve stimulator, microstimulator,or in any other neural stimulator configured to treat urinaryincontinence, sleep apnea, shoulder sublaxation, headache, etc.

Turning first to FIG. 1, an exemplary SCM system 10 generally includes aplurality (in this case, two) of implantable neuromodulation leads 12,an implantable pulse generator (IPG) 14, an external remote controllerRC 16, a clinician's programmer (CP) 18, an external trial modulator(ETM) 20, and an external charger 22.

The IPG 14 is physically connected via one or more percutaneous leadextensions 24 to the neuromodulation leads 12, which carry a pluralityof electrodes 26 arranged in an array. In the illustrated embodiment,the neuromodulation leads 12 are percutaneous leads, and to this end,the electrodes 26 are arranged in-line along the neuromodulation leads12. The number of neuromodulation leads 12 illustrated is two, althoughany suitable number of neuromodulation leads 12 can be provided,including only one. Alternatively, a surgical paddle lead can be used inplace of one or more of the percutaneous leads. As will be described infurther detail below, the IPG 14 includes pulse generation circuitrythat delivers electrical modulation energy in the form of a pulsedelectrical waveform (i.e., a temporal series of electrical pulses) tothe electrode array 26 in accordance with a set of modulationparameters.

The ETM 20 may also be physically connected via the percutaneous leadextensions 28 and external cable 30 to the neuromodulation leads 12. TheETM 20, which has similar pulse generation circuitry as the IPG 14, alsodelivers electrical modulation energy in the form of a pulse electricalwaveform to the electrode array 26 accordance with a set of modulationparameters. The major difference between the ETM 20 and the IPG 14 isthat the ETM 20 is a non-implantable device that is used on a trialbasis after the neuromodulation leads 12 have been implanted and priorto implantation of the IPG 14, to test the responsiveness of themodulation that is to be provided. Thus, any functions described hereinwith respect to the IPG 14 can likewise be performed with respect to theETM 20. For purposes of brevity, the details of the ETM 20 will not bedescribed herein.

The RC 16 may be used to telemetrically control the ETM 20 via abi-directional RF communications link 32. Once the IPG 14 andneuromodulation leads 12 are implanted, the RC 16 may be used totelemetrically control the IPG 14 via a bi-directional RF communicationslink 34. Such control allows the IPG 14 to be turned on or off and to beprogrammed with different modulation parameter sets. The IPG 14 may alsobe operated to modify the programmed modulation parameters to activelycontrol the characteristics of the electrical modulation energy outputby the IPG 14. As will be described in further detail below, the CP 18provides clinician detailed modulation parameters for programming theIPG 14 and ETM 20 in the operating room and in follow-up sessions.

The CP 18 may perform this function by indirectly communicating with theIPG 14 or ETM 20, through the RC 16, via an IR communications link 36.Alternatively, the CP 18 may directly communicate with the IPG 14 or ETM20 via an RF communications link (not shown). The clinician detailedmodulation parameters provided by the CP 18 are also used to program theRC 16, so that the modulation parameters can be subsequently modified byoperation of the RC 16 in a stand-alone mode (i.e., without theassistance of the CP 18).

The external charger 22 is a portable device used to transcutaneouslycharge the IPG 14 via an inductive link 38. Once the IPG 14 has beenprogrammed, and its power source has been charged by the externalcharger 22 or otherwise replenished, the IPG 14 may function asprogrammed without the RC 16 or CP 18 being present. For purposes ofbrevity, the details of the external charger 22 will not be describedherein.

For purposes of brevity, the details of the RC 16, ETM 20, and externalcharger 22 will not be described herein. Details of exemplaryembodiments of these devices are disclosed in U.S. Pat. No. 6,895,280,which is expressly incorporated herein by reference.

As shown in FIG. 2, the neuromodulation leads 12 are implanted withinthe spinal column 42 of a patient 40. The preferred placement of theneuromodulation leads 12 is adjacent, i.e., resting upon, the spinalcord area to be stimulated. Due to the lack of space near the locationwhere the neuromodulation leads 12 exit the spinal column 42, the IPG 14is generally implanted in a surgically-made pocket either in the abdomenor above the buttocks. The IPG 14 may, of course, also be implanted inother locations of the patient's body. The lead extension 24 facilitateslocating the IPG 14 away from the exit point of the neuromodulationleads 12. As there shown, the CP 18 communicates with the IPG 14 via theRC 16.

The IPG 14 comprises an outer case 40 for housing the electronic andother components (described in further detail below), and a connector 42to which the proximal ends of the neuromodulation leads 12 mate in amanner that electrically couples the electrodes 26 to the electronicswithin the outer case 40. The outer case 40 is composed of anelectrically conductive, biocompatible material, such as titanium, andforms a hermetically sealed compartment wherein the internal electronicsare protected from the body tissue and fluids. In some cases, the outercase 40 may serve as an electrode.

The IPG 14 includes a pulse generation circuitry that provideselectrical modulation energy to the electrodes 26 in accordance with aset of modulation parameters. Such parameters may include electrodecombinations, which define the electrodes that are activated as anodes(positive), cathodes (negative), and turned off (zero). The modulationparameters may further include pulse amplitude (measured in milliamps orvolts depending on whether the IPG 14 supplies constant current orconstant voltage to the electrodes), pulse width (measured inmicroseconds), pulse rate (measured in pulses per second), duty cycle(pulse width divided by cycle duration), burst rate (measured as themodulation energy on duration X and modulation energy off duration Y),and pulse shape.

With respect to the pulse patterns provided during operation of thesystem 10, electrodes that are selected to transmit or receiveelectrical energy are referred to herein as “activated,” whileelectrodes that are not selected to transmit or receive electricalenergy are referred to herein as “non-activated.” Electrical energydelivery will occur between two (or more) electrodes, one of which maybe the IPG outer case 40. Electrical energy may be transmitted to thetissue in a monopolar or multipolar (for example, bipolar, tripolar andsimilar configurations) fashion or by any other means available.

The IPG 14 may be operated in either a super-threshold delivery mode ora sub-threshold delivery mode. While in the super-threshold deliverymode, the IPG 14 is configured for delivering electrical modulationenergy that provides super-threshold therapy to the patient (in thiscase, causes the patient to perceive paresthesia). For example, anexemplary super-threshold pulse train may be delivered at a relativelyhigh pulse amplitude (e.g., 5 ma), a relatively low pulse rate (e.g.,less than 1500 Hz, preferably less than 500 Hz), and a relatively highpulse width (e.g., greater than 100 μs, preferably greater than 200 μs).

While in the sub-threshold delivery mode, the IPG 14 is configured fordelivering electrical modulation energy that provides sub-thresholdtherapy to the patient (in this case, does not cause the patient toperceive paresthesia). For example, an exemplary sub-threshold pulsetrain may be delivered at a relatively low pulse amplitude (e.g., 2.5ma), a relatively high pulse rate (e.g., greater than 1500 Hz,preferably greater than 2500 Hz), and a relatively low pulse width(e.g., less than 100 μs, preferably less than 50 μs).

Referring now to FIG. 3, the external features of the neuromodulationleads 12 and the IPG 14 will be briefly described. One of theneuromodulation leads 12 a has eight electrodes 26 (labeled E1-E8), andthe other neuromodulation lead 12 b has eight electrodes 26 (labeledE9-E16). The actual number and shape of leads and electrodes will, ofcourse, vary according to the intended application. The IPG 14 comprisesan outer case 44 for housing the electronic and other components(described in further detail below), and a connector 46 to which theproximal ends of the neuromodulation leads 12 mates in a manner thatelectrically couples the electrodes 26 to the electronics within theouter case 44. The outer case 44 is composed of an electricallyconductive, biocompatible material, such as titanium, and forms ahermetically sealed compartment wherein the internal electronics areprotected from the body tissue and fluids. In some cases, the outer case44 may serve as an electrode.

The IPG 14 comprises electronic components, such as acontroller/processor (e.g., a microcontroller) 48, memory 50, a battery52, telemetry circuitry 54, monitoring circuitry 56, modulation outputcircuitry 58, and other suitable components known to those skilled inthe art. The microcontroller 48 executes a suitable program stored inmemory 50, for directing and controlling the neuromodulation performedby IPG 14. Telemetry circuitry 54, including an antenna (not shown), isconfigured for receiving programming data (e.g., the operating programand/or modulation parameters) from the RC 16 and/or CP 18 in anappropriate modulated carrier signal, which the programming data is thenstored in the memory (not shown). The telemetry circuitry 54 is alsoconfigured for transmitting status data to the RC 16 and/or CP 18 in anappropriate modulated carrier signal. The battery 52, which may be arechargeable lithium-ion or lithium-ion polymer battery, providesoperating power to IPG 14. The monitoring circuitry 56 is configured formonitoring the present capacity level of the battery 43.

The modulation output circuitry 58 provides electrical modulation energyin the form of a pulsed electrical waveform to the electrodes 26 inaccordance with a set of modulation parameters programmed into the IPG14. Such modulation parameters may comprise electrode combinations,which define the electrodes that are activated as anodes (positive),cathodes (negative), and turned off (zero), percentage of modulationenergy assigned to each electrode (fractionalized electrodeconfigurations), and electrical pulse parameters, which define the pulseamplitude (measured in milliamps or volts depending on whether the IPG14 supplies constant current or constant voltage to the electrode array26), pulse width (measured in microseconds), pulse rate (measured inpulses per second), and burst rate (measured as the modulation onduration X and modulation off duration Y).

Electrical modulation will occur between two (or more) activatedelectrodes, one of which may be the IPG case 44. Modulation energy maybe transmitted to the tissue in a monopolar or multipolar (e.g.,bipolar, tripolar, etc.) fashion. Monopolar modulation occurs when aselected one of the lead electrodes 26 is activated along with the caseof the IPG 14, so that modulation energy is transmitted between theselected electrode 26 and case. Bipolar modulation occurs when two ofthe lead electrodes 26 are activated as anode and cathode, so thatmodulation energy is transmitted between the selected electrodes 26. Forexample, electrode E3 on the first lead 12 a may be activated as ananode at the same time that electrode E11 on the second lead 12 b isactivated as a cathode. Tripolar modulation occurs when three of thelead electrodes 26 are activated, two as anodes and the remaining one asa cathode, or two as cathodes and the remaining one as an anode. Forexample, electrodes E4 and E5 on the first lead 12 a may be activated asanodes at the same time that electrode E12 on the second lead 12 b isactivated as a cathode.

Any of the electrodes E1-E16 and case electrode may be assigned to up tok possible groups or timing “channels.” In one embodiment, k may equalfour. The timing channel identifies which electrodes are selected tosynchronously source or sink current to create an electric field in thetissue to be stimulated. Amplitudes and polarities of electrodes on achannel may vary. In particular, the electrodes can be selected to bepositive (sourcing current), negative (sinking current), or off (nocurrent) polarity in any of the k timing channels.

The modulation energy may be delivered between a specified group ofelectrodes as monophasic electrical energy or multiphasic electricalenergy. As illustrated in FIG. 4, monophasic electrical energy takes theform of an electrical pulse train that includes either all negativepulses (cathodic), or alternatively all positive pulses (anodic).

Multiphasic electrical energy includes a series of pulses that alternatebetween positive and negative. For example, as illustrated in FIGS. 5aand 5b , multiphasic electrical energy may include a series of biphasicpulses, with each biphasic pulse including a cathodic (negative)modulation phase and an anodic (positive) charge recovery pulse phasethat is generated after the modulation phase to prevent direct currentcharge transfer through the tissue, thereby avoiding electrodedegradation and cell trauma. That is, charge is conveyed through theelectrode-tissue interface via current at an electrode during amodulation period (the length of the modulation phase), and then pulledback off the electrode-tissue interface via an oppositely polarizedcurrent at the same electrode during a recharge period (the length ofthe charge recovery phase).

The second phase may be an active charge recovery phase (FIG. 5a ),wherein electrical current is actively conveyed through the electrodevia current or voltage sources, or the second phase may be a passivecharge recovery phase (FIG. 5b ), wherein electrical current ispassively conveyed through the electrode via redistribution of thecharge flowing from coupling capacitances present in the circuit. Usingactive recharge, as opposed to passive recharge, allows faster recharge,while avoiding the charge imbalance that could otherwise occur. Anotherelectrical pulse parameter in the form of an interphase can define thetime period between the pulses of the biphasic pulse (measured inmicroseconds). Although the modulation and charge recovery phases of thebiphasic pulses illustrated in FIGS. 5a and 5b are cathodic and anodic,respectively, it should be appreciated that the modulation and chargerecovery pulses of biphasic pulses may be anodic and cathodic,respectively, depending upon the desired therapeutic result.

In the illustrated embodiment, IPG 14 can individually control themagnitude of electrical current flowing through each of the electrodes.In this case, it is preferred to have a current generator, whereinindividual current-regulated amplitudes from independent current sourcesfor each electrode may be selectively generated. Although this system isoptimal to take advantage of the invention, other neuromodulators thatmay be used with the invention include neuromodulators having voltageregulated outputs. While individually programmable electrode amplitudesare optimal to achieve fine control, a single output source switchedacross electrodes may also be used, although with less fine control inprogramming. Mixed current and voltage regulated devices may also beused with the invention. Further details discussing the detailedstructure and function of IPGs are described more fully in U.S. Pat.Nos. 6,516,227 and 6,993,384, which are expressly incorporated herein byreference.

It should be noted that rather than an IPG, the SCM system 10 mayalternatively utilize an implantable receiver-stimulator (not shown)connected to the neuromodulation leads 12. In this case, the powersource, e.g., a battery, for powering the implanted receiver, as well ascontrol circuitry to command the receiver-stimulator, will be containedin an external controller inductively coupled to the receiver-stimulatorvia an electromagnetic link. Data/power signals are transcutaneouslycoupled from a cable-connected transmission coil placed over theimplanted receiver-modulator. The implanted receiver-modulator receivesthe signal and generates the modulation in accordance with the controlsignals.

More significant to the present inventions, since the user cannot relyon the patient's perception of paresthesia to select the proper pulseamplitude, the SCM system 10 is configured for automatically determiningan appropriate pulse amplitude for a desired sub-threshold modulationprogram based on a stored algorithm that accounts for a longitudinallocation of the implanted neuromodulation lead 12. Thus, instead ofmanually testing out various pulse amplitudes in an effort to find anoptimal pulse amplitude for sub-threshold therapy, the user may rely onthe automatically generated pulse amplitude, thereby making theprogramming process more efficient and time-effective.

Typically, the pulse amplitude for sub-threshold modulation therapy iscalculated as a function (e.g., percentage) of the perception threshold(i.e., the amplitude at which the patient perceives paresthesia). Sincethe goal of sub-threshold modulation therapy is to provide therapywithout inducing paresthesia, the sub-threshold amplitude is purposelykept lower than the perception threshold; however, it cannot be so lowthat the patient receives no therapy at all from the lowered amplitude.For example, the sub-threshold amplitude may be calculated to be 70% ofthe perception threshold. Or, in another example, the sub-thresholdamplitude may be 50% of the perception threshold.

It should be appreciated that the same percentage of the perceptionthreshold may not be equally effective in all situations. For example,sub-threshold therapy having a pulse amplitude of 50% of the perceptionthreshold may be effective in one situation, but may not be effective inanother. While the exact mechanisms are not understood, it has beengenerally observed that a lower percentage of the perception thresholdis effective for sub-threshold modulation therapy when the implantedneuromodulation lead 12 is located at an upper region of the spinal cordas compared to when the implanted neuromodulation lead 12 is implantedat a lower region of the spinal cord. In other words, moving down thespinal cord in the caudal direction, a sub-threshold amplitudecalculated based on a higher percentage of the perception threshold istypically required for effective sub-threshold therapy.

One theory for this pattern may relate to the amount of gray matterfound in the spinal cord at different sections of the spinal cord. As ageneral rule, the presence of more gray matter means that there are morenerve endings in that particular region, thus making it more likely thatneural tissue will get directly stimulated. For example, a smallerpercentage of the perception threshold is appropriate when theneuromodulation lead 12 is implanted in the thoracic region as comparedto when the neuromodulation lead 12 is implanted in the sacral region.Based on this observed pattern, the SCM system 10 is configured forautomatically selecting an appropriate percentage of the perceptionthreshold based on the longitudinal location of the implantedneuromodulation lead 12. It should be appreciated that the user mayeither rely on the automatically generated percentage, or instead treatit as a suggestion, based on which to program the IPG 14 with theappropriate modulation parameters for sub-threshold modulation therapy.

In practice, the user performs these programming sessions of the IPG 14on the CP 18. As shown in FIG. 6, the overall appearance of the CP 18 isthat of a laptop personal computer (PC), and in fact, may be implementedusing a PC that has been appropriately configured to include adirectional-programming device and programmed to perform the functionsdescribed herein. Alternatively, the CP 18 may take the form of amini-computer, personal digital assistant (PDA), etc., or even a remotecontrol (RC) with expanded functionality. Thus, the programmingmethodologies can be performed by executing software instructionscontained within the CP 18. Alternatively, such programmingmethodologies can be performed using firmware or hardware. In any event,the CP 18 may actively control the characteristics of the electricalmodulation generated by the IPG 14 to allow the optimum modulationparameters to be determined based on patient feedback and forsubsequently programming the IPG 14 with the optimum modulationparameter.

To allow the user to perform these functions, the CP 18 includes a userinput device (e.g., a mouse 76 and a keyboard 78), and a programmingdisplay screen 80 housed in a case 82. It is to be understood that inaddition to, or in lieu of, the mouse 76, other directional programmingdevices may be used, such as a trackball, touchpad, joystick, ordirectional keys included as part of the keys associated with thekeyboard 78.

In the illustrated embodiment described below, the display screen 80takes the form of a conventional screen, in which case, a virtualpointing device, such as a cursor controlled by a mouse, joy stick,trackball, etc., can be used to manipulate graphical objects on thedisplay screen 80. In alternative embodiments, the display screen 80takes the form of a digitizer touch screen, which may either passive oractive. Further details discussing the use of a digitizer screen forprogramming are set forth in U.S. Provisional Patent Application Ser.No. 61/561,760, entitled “Technique for Linking Electrodes Togetherduring Programming of Neurostimulation System,” which is expresslyincorporated herein by reference.

Referring now to FIG. 6, the CP 18 includes a controller/processor 68(e.g., a central processor unit (CPU)) and memory 70 that stores aprogramming package 72, which can be executed by thecontroller/processor 68 to allow the user to program the IPG 14 and RC16. The CP 18 further includes a user input device 74 (such as the mouse76 or the keyboard 78 described above) to provide user commands.Notably, while the controller/processor 68 is shown in FIG. 6 as asingle device, the processing functions and controlling functions can beperformed by a separate controller and processor. Thus, it can beappreciated that the controlling functions described below as beingperformed by the CP 18 can be performed by a controller, and theprocessing functions described below as being performed by the CP 18 canbe performed by the microcontroller 48 of the IPG 14 or the processor ofthe RC 16.

Execution of the programming package 72 by the controller/processor 68provides a multitude of display screens (not shown) that can benavigated through via use of the mouse 76. These display screens allowthe clinician to, among other functions, to select or enter patientprofile information (e.g., name, birth date, patient identification,physician, diagnosis, and address), enter procedure information (e.g.,programming/follow-up, implant trial system, implant IPG, implant IPGand lead(s), replace IPG, replace IPG and leads, replace or reviseleads, explant, etc.), define the configuration and orientation of theleads, initiate and control the electrical modulation energy output bythe neuromodulation leads 12, and select and program the IPG 14 withmodulation parameters in both a surgical setting and a clinical setting.Further details discussing the above-described CP functions aredisclosed in U.S. patent application Ser. No. 12/501,282, now issued asU.S. Pat. No. 9,278,222, entitled “System and Method for ConvertingTissue Stimulation Programs in a Format Usable by an Electrical CurrentSteering Navigator,” and U.S. patent application Ser. No. 12/614,942,now U.S. Patent Publication No. 2010/0121409, entitled “System andMethod for Determining Appropriate Steering Tables for DistributingModulation energy Among Multiple Neuromodulation Electrodes,” which areexpressly incorporated herein by reference. Execution of the programmingpackage 72 provides a user interface that conveniently allows a user toprogram the IPG 14.

Referring now to FIG. 7, a programming screen 100 that can be generatedby the CP 18 to allow a user to program the IPG 14 will be described. Inthe illustrated embodiment, the programming screen 100 comprises threepanels: a program selection panel 102, a lead display panel 104, and amodulation parameter adjustment panel 106. Some embodiments of theprogramming screen 100 may allow for closing and expanding one or bothof the lead display panel 102 and the parameter adjustment panel 106 byclicking on the tab 108 (to show or hide the parameter adjustment panel106) or the tab 110 (to show or hide the full view of both the leadselection panel 104 and the parameter adjustment panel 106).

The program selection panel 102 provides information about modulationprograms and coverage areas that have been, or may be, defined for theIPG 14. In particular, the program selection panel 102 includes acarousel 112 on which a plurality of modulation programs 114 (in thiscase, up to sixteen) may be displayed and selected. The programselection panel 102 further includes a selected program status field 116indicating the number of the modulation program 114 that is currentlyselected (any number from “1” to “16”). In the illustrated embodiment,program 1 is the only one currently selected, as indicated by the number“1” in the field 116. The program selection panel 102 further comprisesa name field 118 in which a user may associate a unique name to thecurrently selected modulation program 114.

The program selection panel 102 further comprises a plurality ofcoverage areas 120 (in this case, up to four) with which a plurality ofmodulation parameter sets can respectively be associated to create thecurrently selected modulation program 114 (in this case, program 1).Each coverage area 120 that has been defined includes a designationfield 122 (one of letters “A”-“D”), and an electrical pulse parameterfield 124 displaying the electrical pulse parameters, and specifically,the pulse amplitude, pulse width, and pulse rate, of the modulationparameter set associated with the that coverage area. In this example,only coverage area A is defined for program 1, as indicated by the “A”in the designation field 122. The electrical pulse parameter field 124indicates that a pulse amplitude of 5 mA, a pulse width of 80 μs, and apulse rate of 1600 Hz has been associated with coverage area A.

Each of the defined coverage areas 120 also includes a selection icon126 that can be alternately actuated to activate or deactivate therespective coverage area 120. When a coverage area is activated, anelectrical pulse train is delivered from the IPG 14 to the electrodearray 26 in accordance with the modulation parameter set associated withthat coverage area. Notably, multiple ones of the coverage areas 120 canbe simultaneously activated by actuating the selection icons 126 for therespective coverage areas. In this case, multiple electrical pulsetrains are concurrently delivered from the IPG 14 to the electrode array26 during timing channels in an interleaved fashion in accordance withthe respective modulation parameter sets associated with the coverageareas 120. Thus, each coverage area 120 corresponds to a timing channel.

To the extent that any of the coverage areas 120 have not been defined(in this case, three have not been defined), they include text “click toadd another program area”), indicating that any of these remainingcoverage areas 120 can be selected for association with a modulationparameter set. Once selected, the coverage area 120 will be populatedwith the designation field 122, electrical pulse parameter field 124,and selection icon 126.

The parameter adjustment panel 106 includes a pulse amplitude adjustmentcontrol 136 (expressed in milliamperes (mA)), a pulse width adjustmentcontrol 138 (expressed in microseconds (μs)), and a pulse rateadjustment control 140 (expressed in Hertz (Hz)), which are displayedand actuatable in all the programming modes. Each of the controls136-140 includes a first arrow that can be actuated to decrease thevalue of the respective modulation parameter and a second arrow that canbe actuated to increase the value of the respective modulationparameter. Each of the controls 136-140 also includes a display area fordisplaying the currently selected parameter. In response to theadjustment of any of electrical pulse parameters via manipulation of thegraphical controls in the parameter adjustment panel 106, thecontroller/processor 68 generates a corresponding modulation parameterset (with a new pulse amplitude, new pulse width, or new pulse rate) andtransmits it to the IPG 14 via the telemetry circuitry 54 for use indelivering the modulation energy to the electrodes 26.

The parameter adjustment panel 106 includes a pull-down programming modefield 142 that allows the user to switch between a manual programmingmode, an electronic trolling programming mode, and a navigationprogramming mode. Each of these programming modes allows a user todefine a modulation parameter set for the currently selected coveragearea 120 of the currently selected program 114 via manipulation ofgraphical controls in the parameter adjustment panel 106 describedabove, as well as the various graphical controls described below.

The manual programming mode is designed to allow the user to manuallydefine the fractionalized electrical current for the electrode arraywith maximum flexibility; the electronic trolling programming mode isdesigned to quickly sweep the electrode array using a limited number ofelectrode configurations to gradually steer an electrical field relativeto the neuromodulation leads until the targeted modulation site islocated; and the navigation programming mode is designed to sweep theelectrode array using a wide number of electrode configurations to shapethe electrical field, thereby fine tuning and optimization themodulation coverage for patient comfort.

As shown in FIG. 7, the manual programming mode has been selected. Inthe manual programming mode, each of the electrodes 130 of the graphicalleads 128, as well as the graphical case 132, may be individuallyselected, allowing the clinician to set the polarity (cathode or anode)and the magnitude of the current (percentage) allocated to thatelectrode 130, 132 using graphical controls located in anamplitude/polarity area 144 of the parameter adjustment panel 106.

In particular, a graphical polarity control 146 located in theamplitude/polarity area 144 includes a “+” icon, a “−” icon, and an“OFF” icon, which can be respectively actuated to toggle the selectedelectrode 130, 132 between a positive polarization (anode), a negativepolarization (cathode), and an off-state. An amplitude control 148 inthe amplitude/polarity area 144 includes an arrow that can be actuatedto decrease the magnitude of the fractionalized current of the selectedelectrode 130, 132, and an arrow that can be actuated to increase themagnitude of the fractionalized current of the selected electrode 130,132. The amplitude control 148 also includes a display area thatindicates the adjusted magnitude of the fractionalized current for theselected electrode 134. The amplitude control 148 is preferably disabledif no electrode is visible and selected in the lead display panel 104.In response to the adjustment of fractionalized electrode combinationvia manipulation of the graphical controls in the amplitude/polarityarea 144, the controller/processor 68 generates a correspondingmodulation parameter set (with a new fractionalized electrodecombination) and transmits it to the IPG 14 via the telemetry circuitry54 for use in delivering the modulation energy to the electrodes 26.

In the illustrated embodiment, electrode E1 has been selected as acathode and electrode E3 has been selected as anode with 100% of thecathodic and anodic current allocated to each of them respectively.Although the graphical controls located in the amplitude/polarity area144 can be manipulated for any of the electrodes, a dedicated graphicalcontrol for selecting the polarity and fractionalized current value canbe associated with each of the electrodes, as described in U.S. PatentPublication No. 2012/0290041, entitled “Neurostimulation System withOn-Effector Programmer Control,” which is expressly incorporated hereinby reference.

The parameter adjustment panel 106, when the manual programming mode isselected, also includes an equalization control 150 that can be actuatedto automatically equalize current allocation to all electrodes of apolarity selected by respective “Anode +” and “Cathode −” icons.

Significant to the present inventions, the parameter adjustment panel106 also comprises a sub-threshold amplitude control 180 that can beactuated to automatically generate an appropriate sub-thresholdamplitude based on the longitudinal location of the implantedneuromodulation lead 12. In the illustrated embodiment, actuating thesub-threshold amplitude control 180 will determine the sub-thresholdamplitude for the selected sub-threshold program, “Program 1” as shownin the program selection control 102, having a pulse width of 80 μs andpulse rate of 1600 Hz as shown in the parameter adjustment panel 106. Itshould be appreciated that the user may originally select a pulseamplitude (5 mA as illustrated), which is then automatically modifiedafter the sub-threshold amplitude control 180 is actuated. Thesub-threshold modulation program is typically selected based on thepatient's individual needs and targeted area for neuromodulationtherapy. Although the following discussion will focus on the selectedsub-threshold modulation program (Program 1), it should be appreciatedthat the user may manually select modulation parameters in the parameteradjustment panel 106 without relying on existing programs in the programselection panel 102.

When the sub-threshold modulation amplitude control 180 is actuated, theuser is automatically taken to a sub-threshold modulation amplitudedetermination screen 200 as shown in FIG. 8. The main function of thesub-threshold amplitude determination screen 200 is to determine theperception threshold of the selected sub-threshold modulation program(Program 1, in this case), and to calculate the sub-threshold amplitudebased on the perception threshold and the longitudinal location of theimplanted neuromodulation lead 12.

It should be appreciated that the longitudinal location of the implantedneuromodulation lead 12 is typically determined at the very start of theprogramming process (not illustrated), and once it is determined, it isstored in the memory 70. In the preferred embodiment, the SCM system 10is configured for automatically determining the longitudinal location ofthe implanted neuromodulation lead 12. More specifically, the SCM system10 may be configured to apply image recognition techniques to a storedmedical image (e.g., MRI scan, CT scan, fluoroscopy, etc.) of thepatient's spinal cord, and identify the longitudinal location of theimplanted neuromodulation lead 12 with respect to the spinal cord.

In an alternate embodiment, the SCM system 10 may be configured to aidthe user in determining the longitudinal location of the implantedneuromodulation lead. More specifically, the user may view the storedmedical image of the patient's spinal cord and manually input thelongitudinal location of the neuromodulation lead 12. In either case,the longitudinal location of the neuromodulation lead 12 is stored inthe memory, based on which the following sub-threshold amplitude iscalculated after the perception threshold is determined in thesub-threshold amplitude determination screen 200.

As shown in FIG. 8, the sub-threshold amplitude screen 200 includesgraphical leads 128 having graphical electrodes 130 that illustrate theelectrode combination of the selection program. As per the selectedsub-threshold modulation program, Program 1, graphical electrodes E1 andE3 are shown as being selected. The sub-threshold amplitude screen 200also includes a perception threshold determination panel 240. As shownin the illustrated embodiment, the perception threshold determinationpanel 240 also displays the details of the selected sub-thresholdmodulation program, including electrode combination, pulse width, pulserate, polarity, etc. More importantly, the perception thresholddetermination panel allows the user to determine the perceptionthreshold for the selected sub-threshold modulation program.

To determine the perception threshold, the pulse amplitude isincrementally increased using graphical control 242 until the patientreports a feeling of paresthesia, at which point, the “Set Threshold”control 246 can be actuated such that that particular amplitude value atwhich paresthesia was first perceived is automatically recorded. In theillustrated embodiment, the amplitude has been incrementally increasedto reach a pulse amplitude of 3.8 mA, which is set as the perceptionthreshold.

Based on the determined perception threshold, the CP 18 is configured toautomatically calculate the sub-threshold amplitude for thatsub-threshold modulation program based on the perception threshold andthe determined longitudinal location of the implanted neuromodulationlead 12.

To this end, the SCM system 10 may refer to a stored look-up tablecontaining a list of different longitudinal locations of theneuromodulation lead 12, each of which corresponds to an appropriatepercentage of the perception threshold that can be used to calculate thesub-threshold amplitude. The look-up table typically contains a list ofvertebral levels, each of which encompasses several vertebrae thatcorrespond to the same percentage.

For example, there may be four vertebral levels: cervical level (C1-C7),thoracic level (T1-T12), lumbar level (L1-L5) and sacral level (S1-S5).Or, in another example, the look-up table may be even more granular, andcomprise more vertebral levels to account for more subtle differences:cervical level 1 (C1-C3), cervical level 2 (C4-C7), thoracic level 1(T1-T6), etc. In yet another example, to be even more precise, everyvertebra of the vertebral column might constitute its own vertebrallevel (C1 level, C2 level, C3 level, etc.).

Referring now to FIG. 9, one exemplary embodiment of how the CP 18selects the percentage of the perception threshold based on thelongitudinal location of the implanted neuromodulation lead 12 isillustrated. If the determined longitudinal location of the implantedneuromodulation lead 12 is the cervical region of the vertebral column(C1-C7), the selected percentage of the perception threshold from whichto calculate the sub-threshold amplitude is 30%. If the determinedlongitudinal location of the implanted neuromodulation lead 12 is thethoracic region of the vertebral column (T1-T12), the selectedpercentage of the perception threshold from which to calculate thesub-threshold amplitude is 40%. If the determined longitudinal locationof the implanted neuromodulation lead 12 is the lumbar region of thevertebral column (L1-L5), the selected percentage of the perceptionthreshold from which to calculate the sub-threshold amplitude is 50%.Similarly, if the determined longitudinal location of the implantedneuromodulation lead 12 is the sacral region of the vertebral column(S1-S5), the selected percentage of the perception threshold from whichto calculate the sub-threshold amplitude is 60%.

It should be appreciated that the above mentioned vertebral levels andpercentages are exemplary only, and that different embodiments may useother and/or similar percentages. As a general rule, the percentage forthe cervical region of the spinal cord typically ranges from 20%-60% ofthe perception threshold, the percentage for the thoracic region of thespinal cord typically ranges from 30%-70% of the perception threshold,the percentage for the lumbar region of the spinal cord typically rangesfrom 40%-80% of the perception threshold, and the percentage for thesacral region of the spinal cord typically ranges from 50%-90% of theperception threshold. As mentioned previously, the look-up table may useany percentages that fall within the above mentioned ranges for eachvertebral level in selecting the percentage to be used in calculatingthe sub-threshold amplitude. It should be appreciated that certainembodiments may illustrate the calculated sub-threshold amplitude in thesub-threshold amplitude screen 200, while others may display thecalculated sub-threshold amplitude in the manual programming screen 100.

In the illustrated embodiment, once the perception threshold has beendetermined, the user may actuate the “OK” button 250 to be automaticallytaken back to the manual programming mode screen 100. Assuming that thedetermined longitudinal location of the neuromodulation lead 12 is inthe sacral region, the calculated sub-threshold amplitude is 2.3 mA(i.e., 60% of the perception threshold set at 3.8 mA), as shown in theparameter adjustment panel 102 of the manual programming screen,illustrated in FIG. 10. It should be appreciated that the generatedsub-threshold amplitude may be modified based on user discretion usinggraphical controls 136.

In a preferred embodiment, the sub-threshold amplitude and/or a range ofsub-threshold amplitudes may be additionally stored into the RC 16 suchthat the patient can maintain some control over the programming of theIPG 14 at home. For example, if the patient wants to modify thesub-threshold amplitude (or other modulation parameters), he may easilydo so with the RC 16.

To this end, the acceptable ranges of sub-threshold amplitude for thedetermined longitudinal location of the implanted neuromodulation lead12 may be automatically stored in the RC 16. For example, if thedetermined location of the neuromodulation lead 12 is the sacral region,even though the sub-threshold amplitude is currently set at 60% of theperception threshold in the illustrated embodiment as per the look-uptable of FIG. 9, the patient may be able to modify the sub-thresholdamplitude as long as it stays within the preferred range of 50%-90% ofthe perception threshold for the sacral region (i.e., 1.9 mA to 3.42mA). Or, if the determined location of the neuromodulation lead 12 isthe cervical region, even though the sub-threshold amplitude may be setat 1.14 mA (not shown) the patient may be able to modify thesub-threshold amplitude as long as it stays within the preferred rangeof 20%-60% of the perception threshold for the cervical region (i.e.,0.76 mA to 3.04 mA). The ranges of the thoracic and lumbar regions maybe similarly stored to allow for modification of the sub-thresholdamplitude based on patient discretion.

In an alternate embodiment, the user may define (not illustrated), aminimum amplitude level and a maximum amplitude level such that thepatient, at his/her own discretion, is able to adjust the sub-thresholdamplitude within a range. For example, assuming that the sub-thresholdamplitude level is set at 60% of the perception threshold, the minimumamplitude level may be defined as 50% of the perception threshold, andthe maximum amplitude may be defined as 70% of the perception threshold.Or, in another example, if the user wants therapy to remain at a tighterrange, the minimum amplitude may be set at 55% of the perceptionthreshold and the maximum amplitude may be set at 65% of the perceptionthreshold.

Thus, by automatically selecting the appropriate percentage of theperception threshold from which to calculate the sub-thresholdamplitude, the SCM system 10 accounts for the differences in neuraltissue along the spinal cord, thereby making the process of finding anoptimal sub-threshold modulation regimen for the patient easier and moreefficient.

Although the illustrated embodiments have focused on using the manualprogramming mode, it should be appreciated that any of the otherprogramming modes of the CP 18 may also be similarly used.

Although particular embodiments of the present inventions have beenshown and described, it will be understood that it is not intended tolimit the present inventions to the preferred embodiments, and it willbe obvious to those skilled in the art that various changes andmodifications may be made without departing from the spirit and scope ofthe present inventions. Thus, the present inventions are intended tocover alternatives, modifications, and equivalents, which may beincluded within the spirit and scope of the present inventions asdefined by the claims.

What is claimed is:
 1. A neuromodulation system for use with aneuromodulation lead having at least one electrode configured for beingimplanted along a spinal cord of a patient, the system comprising:control/processing circuitry configured to use a longitudinal locationof the at least one electrode relative to the spinal cord to determine avalue of a neuromodulation parameter for delivering subthresholdmodulation energy; and modulation output circuitry configured to deliverthe sub-threshold modulation energy to the at least one electrode. 2.The neuromodulation system of claim 1, wherein the control/processingcircuitry is configured to determine the longitudinal location of the atleast one electrode relative to the spinal cord.
 3. The neuromodulationsystem of claim 2, wherein the longitudinal location of the at least oneelectrode relative to the spinal cord is determined based on alongitudinal location of the neuromodulation lead relative to the spinalcord.
 4. The neuromodulation system of claim 1, further comprising auser interface configured to receive as a user input the longitudinallocation of the at least one electrode relative to the spinal cord. 5.The neuromodulation system of claim 1, wherein the at least oneelectrode comprises more than one electrode, and the control/processingcircuitry is configured to compute the value of the neuromodulationparameter as a function of a fractionalized electrode configuration thatdetermines modulation energy contributions assigned to each of the morethan one electrode.
 6. The neuromodulation system of claim 5, whereinthe value is a first modulation energy contribution when thelongitudinal location is in a first region of the spinal cord, and thevalue is a second modulation energy contribution when the longitudinallocation is in a second region of the spinal cord, wherein the secondmodulation energy contribution is higher than the first modulationenergy contribution, and the second region of the spinal cord is caudalrelative to the first region of the spinal cord.
 7. The neuromodulationsystem of claim 5, wherein the value is a first modulation energycontribution when the longitudinal location is in a cervical region ofthe spinal cord, the value is a second modulation energy contributionwhen the longitudinal location is in a thoracic region of the spinalcord, the value is a third modulation energy contribution when thelongitudinal location is in a lumbar region of the spinal cord, and thevalue is a fourth modulation energy contribution when the longitudinallocation is in a sacral region of the spinal cord, wherein the secondmodulation energy contribution is greater than the first modulationenergy contribution, the third modulation energy contribution is greaterthan the second modulation energy contribution, and the fourthmodulation energy contribution is greater than the third modulationenergy contribution.
 8. The neuromodulation system of claim 1, furthercomprising memory storing a look-up table containing longitudinallocations and a value of the neuromodulation parameter associated witheach of the longitudinal locations, wherein the control/processingcircuitry is configured to match the longitudinal location of the atleast one electrode relative to the spinal cord with one of thelocations stored in the look-up table and select the value of theneuromodulation parameter associated with the matched location.
 9. Anexternal controller for use with a neuromodulation device coupleable toat least one electrode, the external controller comprising: a userinterface configured to receive user input; and control/processingcircuitry configured to select a neuromodulation parameter value basedon a longitudinal location of the at least one electrode relative to aspinal cord.
 10. The external controller of claim 9, wherein thecontrol/processing circuitry is configured to determine the longitudinallocation of the at least one electrode relative to the spinal cord. 11.The external controller of claim 10, wherein the longitudinal locationof the at least one electrode relative to the spinal cord is determinedbased on a longitudinal location of the neuromodulation lead relative tothe spinal cord.
 12. The external controller of claim 9, wherein theuser interface is further configured to receive as a user input thelongitudinal location of the at least one electrode relative to thespinal cord.
 13. The external controller of claim 9, wherein the atleast one electrode comprises more than one electrode, and thecontrol/processing circuitry is configured to compute theneuromodulation parameter value as a function of a fractionalizedelectrode configuration that determines a relative modulation energycontribution assigned to each electrode.
 14. The external controller ofclaim 12, wherein the neuromodulation parameter value is a firstmodulation energy contribution when the longitudinal location is in afirst region of the spinal cord, and the neuromodulation parameter valueis a second modulation energy contribution when the longitudinallocation is in a second region of the spinal cord, wherein the secondmodulation energy contribution is higher than the first modulationenergy contribution, and the second region of the spinal cord is caudalrelative to the first region of the spinal cord.
 15. The externalcontroller of claim 12, wherein the neuromodulation parameter value is afirst modulation energy contribution when the longitudinal location isin a cervical region of the spinal cord, the neuromodulation parametervalue is a second modulation energy contribution when the longitudinallocation is in a thoracic region of the spinal cord, the neuromodulationparameter value is a third modulation energy contribution when thelongitudinal location is in a lumbar region of the spinal cord, and theneuromodulation parameter value is a fourth modulation energycontribution when the longitudinal location is in a sacral region of thespinal cord, wherein the second modulation energy contribution isgreater than the first modulation energy contribution, the thirdmodulation energy contribution is greater than the second modulationenergy contribution, and the fourth modulation energy contribution isgreater than the third modulation energy contribution.
 16. The externalcontroller of claim 9, further comprising memory storing a look-up tablecontaining longitudinal locations and a neuromodulation parameter valueassociated with each of the longitudinal locations, wherein thecontrol/processing circuitry is configured to match the longitudinallocation of the at least one electrode relative to the spinal cord withone of the locations stored in the look-up table and select theneuromodulation parameter value associated with the matched location.17. A method, comprising: determining a neuromodulation parameter valuefor subthreshold modulation energy using a longitudinal location of atleast one electrode relative to the spinal cord; and providing asubthreshold modulation therapy using the at least one electrode,including delivering the sub-threshold modulation energy at thedetermined neuromodulation parameter value.
 18. The method of claim 17,further comprising: determining the longitudinal location of the atleast one electrode relative to the spinal cord.
 19. The method of claim17, further comprising: receiving as user input the longitudinallocation of the at least one electrode relative to the spinal cord. 20.The method of claim 17, wherein delivering the sub-threshold modulationenergy includes using electrodes to deliver the sub-threshold modulationenergy, the method further comprising computing the neuromodulationparameter value as a function of a fractionalized electrodeconfiguration that determines modulation energy contributions assignedto each electrode.